3d semiconductor device and structure

ABSTRACT

A 3D semiconductor device, the device including: a first level including a first single crystal layer and first transistors, where the first transistors each include a single crystal channel; first metal layers interconnecting at least the first transistors; and a second level including a second single crystal layer and second transistors, where the second level overlays the first level, where the second transistors are horizontally oriented and include a gate dielectric, where the gate dielectric includes hafnium oxide, where the second level is bonded to the first level, and where the bonded includes oxide to oxide bonds.

CROSS-REFERENCE OF RELATED APPLICATION

This application is a continuation in part of U.S. patent applicationSer. No. 17/114,155, which was filed on Dec. 7, 2020, which is acontinuation in part of U.S. patent application Ser. No. 17/013,823,which was filed on Sep. 7, 2020, and now is U.S. Pat. No. 10,896,931issued on Jan. 19, 2021, which is a continuation in part of U.S. patentapplication Ser. No. 16/409,813, which was filed on May 11, 2019, andnow is U.S. Pat. No. 10,825,864 issued on Nov. 3, 2020, which is acontinuation in part of U.S. patent application Ser. No. 15/803,732,which was filed on Nov. 3, 2017, and now is U.S. Pat. No. 10,290,682issued on May 14, 2019, which is a continuation in part of U.S. patentapplication Ser. No. 14/555,494, which was filed on Nov. 26, 2014, andnow is U.S. Pat. No. 9,818,800 issued on Nov. 14, 2017, which is acontinuation of U.S. patent application Ser. No. 13/246,157, which wasfiled on Sep. 27, 2011 and now is U.S. Pat. No. 8,956,959 issued on Feb.17, 2015, which is a continuation of U.S. patent application Ser. No.13/173,999, which was filed on Jun. 30, 2011 and now is U.S. Pat. No.8,203,148 issued on Jun. 19, 2012, which is a continuation of U.S.patent application Ser. No. 12/901,890, which was filed on Oct. 11,2010, and now is U.S. Pat. No. 8,026,521 issued on Sep. 27, 2011, theentire contents of the foregoing are incorporated by reference herein.

BACKGROUND OF THE INVENTION 1. Field of the Invention

This invention describes applications of monolithic 3D integration to atleast semiconductor chips performing logic and memory functions.

2. Discussion of Background Art

Over the past 40 years, one has seen a dramatic increase infunctionality and performance of Integrated Circuits (ICs). This haslargely been due to the phenomenon of “scaling” i.e. component sizeswithin ICs have been reduced (“scaled”) with every successive generationof technology. There are two main classes of components in ComplimentaryMetal Oxide Semiconductor (CMOS) ICs, namely transistors and wires. With“scaling”, transistor performance and density typically improve and thishas contributed to the previously-mentioned increases in IC performanceand functionality. However, wires (interconnects) that connect togethertransistors degrade in performance with “scaling”. The situation todayis that wires dominate performance, functionality and power consumptionof ICs.

3D stacking of semiconductor chips is one avenue to tackle issues withwires. By arranging transistors in 3 dimensions instead of 2 dimensions(as was the case in the 1990s), one can place transistors in ICs closerto each other. This reduces wire lengths and keeps wiring delay low.However, there are many barriers to practical implementation of 3Dstacked chips. These include:

-   -   Constructing transistors in ICs typically require high        temperatures (higher than ˜700° C.) while wiring levels are        constructed at low temperatures (lower than ˜400° C.). Copper or        Aluminum wiring levels, in fact, can get damaged when exposed to        temperatures higher than ˜400° C. If one would like to arrange        transistors in 3 dimensions along with wires, it has the        challenge described below. For example, let us consider a 2        layer stack of transistors and wires i.e. Bottom Transistor        Layer, above it Bottom Wiring Layer, above it Top Transistor        Layer and above it Top Wiring Layer. When the Top Transistor        Layer is constructed using Temperatures higher than 700° C., it        can damage the Bottom Wiring Layer.    -   Due to the above mentioned problem with forming transistor        layers above wiring layers at temperatures lower than 400° C.,        the semiconductor industry has largely explored alternative        architectures for 3D stacking. In these alternative        architectures, Bottom Transistor Layers, Bottom Wiring Layers        and Contacts to the Top Layer are constructed on one silicon        wafer. Top Transistor Layers, Top Wiring Layers and Contacts to        the Bottom Layer are constructed on another silicon wafer. These        two wafers are bonded to each other and contacts are aligned,        bonded and connected to each other as well. Unfortunately, the        size of Contacts to the other Layer is large and the number of        these Contacts is small. In fact, prototypes of 3D stacked chips        today utilize as few as 10,000 connections between two layers,        compared to billions of connections within a layer. This low        connectivity between layers is because of two reasons: (i)        Landing pad size needs to be relatively large due to alignment        issues during wafer bonding. These could be due to many reasons,        including bowing of wafers to be bonded to each other, thermal        expansion differences between the two wafers, and lithographic        or placement misalignment. This misalignment between two wafers        limits the minimum contact landing pad area for electrical        connection between two layers; (ii) The contact size needs to be        relatively large. Forming contacts to another stacked wafer        typically involves having a Through-Silicon Via (TSV) on a chip.        Etching deep holes in silicon with small lateral dimensions and        filling them with metal to form TSVs is not easy. This places a        restriction on lateral dimensions of TSVs, which in turn impacts        TSV density and contact density to another stacked layer.        Therefore, connectivity between two wafers is limited.

It is highly desirable to circumvent these issues and build 3D stackedsemiconductor chips with a high-density of connections between layers.To achieve this goal, it is sufficient that one of three requirementsmust be met: (1) A technology to construct high-performance transistorswith processing temperatures below ˜400° C.; (2) A technology wherestandard transistors are fabricated in a pattern, which allows for highdensity connectivity despite the misalignment between the two bondedwafers; and (3) A chip architecture where process temperature increasebeyond 400° C. for the transistors in the top layer does not degrade thecharacteristics or reliability of the bottom transistors and wiringappreciably. This patent application describes approaches to addressoptions (1), (2) and (3) in the detailed description section. In therest of this section, background art that has previously tried toaddress options (1), (2) and (3) will be described.

There are many techniques to construct 3D stacked integrated circuits orchips including:

-   -   Through-silicon via (TSV) technology: Multiple layers of        transistors (with or without wiring levels) can be constructed        separately. Following this, they can be bonded to each other and        connected to each other with through-silicon vias (TSVs).    -   Monolithic 3D technology: With this approach, multiple layers of        transistors and wires can be monolithically constructed. Some        monolithic 3D and 3DIC approaches are described in U.S. Pat.        Nos. 8,273,610, 8,298,875, 8,362,482, 8,378,715, 8,379,458,        8,450,804, 8,557,632, 8,574,929, 8,581,349, 8,642,416,        8,669,778, 8,674,470, 8,687,399, 8,742,476, 8,803,206,        8,836,073, 8,902,663, 8,994,404, 9,023,688, 9,029,173,        9,030,858, 9,117,749, 9,142,553, 9,219,005, 9,385,058,        9,406,670, 9,460,978, 9,509,313, 9,640,531, 9,691,760,        9,711,407, 9,721,927, 9,799,761, 9,871,034, 9,953,870,        9,953,994, 10,014,292, 10,014,318, 10,515,981, 10,892,016; and        pending U.S. patent application Publications and applications,        14/642,724, 15/150,395, 15/173,686, 16/337,665, 16/558,304,        16/649,660, 16/836,659, 17/151,867, 62/651,722; 62/681,249,        62/713,345, 62/770,751, 62/952,222, 62/824,288, 63/075,067,        63/091,307, 63/115,000, 2020/0013791, 16/558,304; and PCT        Applications (and Publications): PCT/US2010/052093,        PCT/US2011/042071 (WO2012/015550), PCT/US2016/52726        (WO2017053329), PCT/US2017/052359 (WO2018/071143),        PCT/US2018/016759 (WO2018144957), and PCT/US2018/52332(WO        2019/060798). The entire contents of the foregoing patents,        publications, and applications are incorporated herein by        reference.    -   Electro-Optics: There is also work done for integrated        monolithic 3D including layers of different crystals, such as        U.S. Pat. Nos. 8,283,215, 8,163,581, 8,753,913, 8,823,122,        9,197,804, 9,419,031, 9,941,319, 10,679,977, and 10,943,934. The        entire contents of the foregoing patents, publications, and        applications are incorporated by reference herein.    -   In addition, the entire contents of U.S. Pat. Nos. 8,026,521,        8,203,148, 8,956,959, 9,818,800, 10,290,682, and 10,825,864,        U.S. patent application publication N/A, and U.S. patent        application Ser. No. 17/013,823 are incorporated herein by        reference.

U.S. Pat. No. 7,052,941 from Sang-Yun Lee (“S-Y Lee”) describes methodsto construct vertical transistors above wiring layers at less than 400°C. In these single crystal Si transistors, current flow in thetransistor's channel region is in the vertical direction. Unfortunately,however, almost all semiconductor devices in the market today (logic,DRAM, flash memory) utilize horizontal (or planar) transistors due totheir many advantages, and it is difficult to convince the industry tomove to vertical transistor technology.

A paper from IBM at the Intl. Electron Devices Meeting in 2005 describesa method to construct transistors for the top stacked layer of a 2 chip3D stack on a separate wafer. This paper is “Enabling SOI-Based AssemblyTechnology for Three-Dimensional (3D) Integrated Circuits (ICs),” IEDMTech. Digest, p. 363 (2005) by A. W. Topol, D. C. La Tulipe, L. Shi, etal. (“Topol”). A process flow is utilized to transfer this toptransistor layer atop the bottom wiring and transistor layers attemperatures less than 400° C. Unfortunately, since transistors arefully formed prior to bonding, this scheme suffers from misalignmentissues. While Topol describes techniques to reduce misalignment errorsin the above paper, the techniques of Topol still suffer frommisalignment errors that limit contact dimensions between two chips inthe stack to >130 nm.

The textbook “Integrated Interconnect Technologies for 3D NanoelectronicSystems” by Bakir and Meindl (“Bakir”) describes a 3D stacked DRAMconcept with horizontal (i.e. planar) transistors. Silicon for stackedtransistors is produced using selective epitaxy technology or laserrecrystallization. Unfortunately, however, these technologies havehigher defect density compared to standard single crystal silicon. Thishigher defect density degrades transistor performance.

In the NAND flash memory industry, several organizations have attemptedto construct 3D stacked memory. These attempts predominantly usetransistors constructed with poly-Si or selective epi technology as wellas charge-trap concepts. References that describe these attempts to 3Dstacked memory include “Integrated Interconnect Technologies for 3DNanoelectronic Systems”, Artech House, 2009 by Bakir and Meindl(“Bakir”), “Bit Cost Scalable Technology with Punch and Plug Process forUltra High Density Flash Memory”, Symp. VLSI Technology Tech. Dig. pp.14-15, 2007 by H. Tanaka, M. Kido, K. Yahashi, et al. (“Tanaka”), “AHighly Scalable 8-Layer 3D Vertical-Gate (VG) TFT NAND Flash UsingJunction-Free Buried Channel BE-SONOS Device,” Symposium on VLSITechnology, 2010 by W. Kim, S. Choi, et al. (“W. Kim”), “A HighlyScalable 8-Layer 3D Vertical-Gate (VG) TFT NAND Flash UsingJunction-Free Buried Channel BE-SONOS Device,” Symposium on VLSITechnology, 2010 by Hang-Ting Lue, et al. (“Lue”) and “Sub-50 nmDual-Gate Thin-Film Transistors for Monolithic 3-D Flash”, IEEE Trans.Elect. Dev., vol. 56, pp. 2703-2710, Nov. 2009 by A. J. Walker(“Walker”). An architecture and technology that utilizes single crystalSilicon using epi growth is described in “A Stacked SONOS Technology, Upto 4 Levels and 6 nm Crystalline Nanowires, with Gate-All-Around orIndependent Gates (DFlash), Suitable for Full 3D Integration”,International Electron Devices Meeting, 2009 by A. Hubert, et al(“Hubert”). However, the approach described by Hubert has somechallenges including use of difficult-to-manufacture nanowiretransistors, higher defect densities due to formation of Si and SiGelayers atop each other, high temperature processing for long times,difficult manufacturing, etc.

It is clear based on the background art mentioned above that inventionof novel technologies for 3D stacked layer and chips will be useful.

SUMMARY

The invention may be directed to at least multilayer or ThreeDimensional Integrated Circuit (3D IC) devices, structures, andfabrication methods.

In one aspect, a 3D semiconductor device, the device including: a firstlevel including a first single crystal layer and first transistors,where the first transistors each include a single crystal channel; firstmetal layers interconnecting at least the first transistors; and asecond level including a second single crystal layer and secondtransistors, where the second level overlays the first level, where thesecond transistors are horizontally oriented and include a gatedielectric, where the gate dielectric includes hafnium oxide, where thesecond level is bonded to the first level, and where the bonded includesoxide to oxide bonds.

In another aspect, a 3D semiconductor device, the device including: afirst level including a first single crystal layer and firsttransistors, where the first transistors each include a single crystalchannel; first metal layers interconnecting at least the firsttransistors; and a second level including a second single crystal layerand second transistors, where the second level overlays the first level,where the second transistors are horizontally oriented, where the atleast one of the second transistors is a Recessed Channel ArrayTransistor (“RCAT”), where the second level is bonded to the firstlevel, and where the bonded includes oxide to oxide bonds.

In another aspect, a 3D semiconductor device, the device including: afirst level including a first single crystal layer and firsttransistors, where the first transistors each include a single crystalchannel; first metal layers interconnecting at least the firsttransistors; a second level including a second single crystal layer andsecond transistors, where the second level overlays the first level; anda second metal layer and a third metal layer, where the second metallayer is disposed above the first metal layer, where the third metallayer is above the second metal layer and below the second singlecrystal layer, where the second metal includes a first thickness and thethird metal includes a second thickness, where the first thickness issignificantly greater than the second thickness, where the second levelis bonded to the first level, and where the bonded includes oxide tooxide bonds.

In another aspect, a 3D semiconductor device, the device including: afirst level including a first single crystal layer and firsttransistors, where the first transistors each include a single crystalchannel; first metal layers interconnecting at least the firsttransistors; and a second level including a second single crystal layerand second transistors, where the second level overlays the first level,where the second transistors are horizontally oriented and includereplacement gate, where the second level is bonded to the first level,and where the bonded includes oxide to oxide bonds.

In another aspect, a 3D semiconductor device, the device including: afirst level including a first single crystal layer and alignment marks;first transistors overlaying the first single crystal layer; and secondtransistors overlaying the first transistors, where the firsttransistors and the second transistors are self-aligned, being processedfollowing the same lithography step, where the second transistorsinclude replacement gate, being processed to replace a poly silicon gateto a metal based gate, where the first level includes third transistorsdisposed below the first transistor, where the third transistors arealigned to the alignment marks, and where the third transistors eachinclude a single crystal channel.

In another aspect, a 3D semiconductor device, the device including: afirst level including a first single crystal layer, first transistors,and second transistors, where the second transistors are overlaying thefirst transistors, and where the first transistors and the secondtransistors are self-aligned, being processed following the samelithography step; and a second level including a second single crystallayer and third transistors, where the second level overlays the firstlevel, where the third transistors are horizontally oriented and includereplacement gate, where the second level is bonded to the first level,and where the bonded includes oxide to oxide bonds.

BRIEF DESCRIPTION OF THE DRAWINGS

Various embodiments of the invention will be understood and appreciatedmore fully from the following detailed description, taken in conjunctionwith the drawings in which:

FIGS. 1A-1C show different types of junction-less transistors (JLT) thatcould be utilized for 3D stacking;

FIGS. 2A-2K show a zero-mask per layer 3D floating body DRAM;

FIGS. 3A-3J show a zero-mask per layer 3D resistive memory with ajunction-less transistor;

FIGS. 4A-4K show an alternative zero-mask per layer 3D resistive memory;

FIGS. 5A-5G show a zero-mask per layer 3D charge-trap memory;

FIGS. 6A-6B show periphery on top of memory layers;

FIGS. 7A-7E show polysilicon select devices for 3D memory and peripheralcircuits at the bottom according to some embodiments of the currentinvention;

FIGS. 8A-8F show polysilicon select devices for 3D memory and peripheralcircuits at the top according to some embodiments of the currentinvention;

FIGS. 9A-9F illustrate a process flow for 3D integrated circuits withgate-last high-k metal gate transistors and face-up layer transfer;

FIGS. 10A-10D depict a process flow for constructing 3D integrated chipsand circuits with misalignment tolerance techniques and repeatingpattern in one direction;

FIGS. 11A-11G illustrate using a carrier wafer for layer transfer;

FIGS. 12A-12K illustrate constructing chips with nMOS and pMOS deviceson either side of the wafer; and

FIG. 13 illustrates constructing transistors with front gates and backgates on either side of the semiconductor layer.

DETAILED DESCRIPTION

Embodiments of the present invention are now described with reference toFIGS. 1A-13, it being appreciated that the figures illustrate thesubject matter not to scale or to measure. Many figures describe processflows for building devices. These process flows, which are essentially asequence of steps for building a device, have many structures, numeralsand labels that are common between two or more adjacent steps. In suchcases, some labels, numerals and structures used for a certain step'sfigure may have been described in previous steps' figures.

FIG. 1A-1D shows that JLTs that can be 3D stacked fall into fourcategories based on the number of gates they use: One-side gated JLTs asshown in FIG. 1A, two-side gated JLTs as shown in FIG. 1B, three-sidegated JLTs as shown in FIG. 1C, and gate-all-around JLTs as shown inFIG. 1D. The JLTS shown may include n+Si 102, gate dielectric 104, gateelectrode 106, n+ source region 108, n+ drain region 110, and n+ regionunder gate 112. As the number of JLT gates increases, the gate gets morecontrol of the channel, thereby reducing leakage of the JLT at 0V.Furthermore, the enhanced gate control can be traded-off for higherdoping (which improves contact resistance to source-drain regions) orbigger JLT cross-sectional areas (which is easier from a processintegration standpoint). However, adding more gates typically increasesprocess complexity.

Some embodiments of this invention may involve floating body DRAM.Background information on floating body DRAM and its operation is givenin “Floating Body RAM Technology and its Scalability to 32 nm Node andBeyond,” Electron Devices Meeting, 2006. IEDM '06. International, vol.,no., pp. 1-4, 11-13 Dec. 2006 by T. Shino, N. Kusunoki, T. Higashi, etal., Overview and future challenges of floating body RAM (FBRAM)technology for 32 nm technology node and beyond, Solid-StateElectronics, Volume 53, Issue 7, Papers Selected from the 38th EuropeanSolid-State Device Research Conference—ESSDERC′08, July 2009, Pages676-683, ISSN 0038-1101, DOI: 10.1016/j.sse.2009.03.010 by TakeshiHamamoto, Takashi Ohsawa, et al., “New Generation of Z-RAM,” ElectronDevices Meeting, 2007. IEDM 2007. IEEE International, vol., no., pp.925-928, 10-12 Dec. 2007 by Okhonin, S.; Nagoga, M.; Carman, E, et al.The above publications are incorporated herein by reference.

FIG. 2A-K describe a process flow to construct a horizontally-orientedmonolithic 3D DRAM. This monolithic 3D DRAM utilizes the floating bodyeffect and double-gate transistors. No mask is utilized on a“per-memory-layer” basis for the monolithic 3D DRAM concept shown inFIG. 2A-K, and all other masks are shared between different layers. Theprocess flow may include several steps in the following sequence.

Step (A): Peripheral circuits with tungsten wiring 202 are firstconstructed and above this a layer of silicon dioxide 204 is deposited.FIG. 2A shows a drawing illustration after Step (A).Step (B): FIG. 2B illustrates the structure after Step (B). A wafer ofp-Silicon 208 has an oxide layer 206 grown or deposited above it.Following this, hydrogen is implanted into the p-Silicon wafer at acertain depth indicated by 214. Alternatively, some other atomic speciessuch as Helium could be (co-)implanted. This hydrogen implantedp-Silicon wafer 208 forms the top layer 210. The bottom layer 212 mayinclude the peripheral circuits 202 with oxide layer 204. The top layer210 is flipped and bonded to the bottom layer 212 using oxide-to-oxidebonding.Step (C): FIG. 2C illustrates the structure after Step (C). The stack oftop and bottom wafers after Step (B) is cleaved at the hydrogen plane3014 using either a anneal or a sideways mechanical force or othermeans. A CMP process is then conducted. A layer of silicon oxide 218 isthen deposited atop the p-Silicon layer 216. At the end of this step, asingle-crystal p-Si layer 216 exists atop the peripheral circuits, andthis has been achieved using layer-transfer techniques.Step (D): FIG. 2D illustrates the structure after Step (D). Usingmethods similar to Step (B) and (C), multiple p-silicon layers 220 areformed with silicon oxide layers in between.Step (E): FIG. 2E illustrates the structure after Step (E). Lithographyand etch processes are then utilized to make a structure as shown in thefigure, including layer regions of p-silicon 221 and associatedisolation/bonding oxides 222.Step (F): FIG. 2F illustrates the structure after Step (F). Gatedielectric 226 and gate electrode 224 are then deposited following whicha CMP is done to planarize the gate electrode 224 regions. Lithographyand etch are utilized to define gate regions.Step (G): FIG. 2G illustrates the structure after Step (G). Using thehard mask defined in Step (F), p-regions not covered by the gate areimplanted to form n+ silicon regions 228. Spacers are utilized duringthis multi-step implantation process and layers of silicon present indifferent layers of the stack have different spacer widths to accountfor lateral straggle of buried layer implants. Bottom layers could havelarger spacer widths than top layers. A thermal annealing step, such asa RTA or spike anneal or laser anneal or flash anneal, is then conductedto activate n+ doped regions.Step (H): FIG. 2H illustrates the structure after Step (H). A siliconoxide layer 230 is then deposited and planarized. For clarity, thesilicon oxide layer is shown transparent, along with word-line (WL) 232and source-line (SL) 234 regions.Step (I): FIG. 2I illustrates the structure after Step (I). Bit-line(BL) contacts 236 are formed by etching and deposition. These BLcontacts are shared among all layers of memory.Step (J): FIG. 2J illustrates the structure after Step (J). BLs 238 arethen constructed. Contacts are made to BLs, WLs and SLs of the memoryarray at its edges. SL contacts can be made into stair-like structuresusing techniques described in “Bit Cost Scalable Technology with Punchand Plug Process for Ultra High Density Flash Memory,” VLSI Technology,2007 IEEE Symposium on, vol., no., pp. 14-15, 12-14 Jun. 2007 by Tanaka,H.; Kido, M.; Yahashi, K.; Oomura, M.; et al., following which contactscan be constructed to them. Formation of stair-like structures for SLscould be done in steps prior to Step (J) as well.FIG. 2K shows cross-sectional views of the array for clarity.Double-gated transistors may be utilized along with the floating bodyeffect for storing information.A floating-body DRAM has thus been constructed, with (1)horizontally-oriented transistors—i.e. current flowing in substantiallythe horizontal direction in transistor channels (2) some of the memorycell control lines, e.g., source-lines SL, constructed of heavily dopedsilicon and embedded in the memory cell layer, (3) side gatessimultaneously deposited over multiple memory layers, and (4)monocrystalline (or single-crystal) silicon layers obtained by layertransfer techniques such as ion-cut.

With the explanations for the formation of monolithic 3D DRAM withion-cut in this section, it is clear to one skilled in the art thatalternative implementations are possible. BL and SL nomenclature hasbeen used for two terminals of the 3D DRAM array, and this nomenclaturecan be interchanged. Each gate of the double gate 3D DRAM can beindependently controlled for better control of the memory cell. Toimplement these changes, the process steps in FIG. 2 may be modified.Moreover, selective epi technology or laser recrystallization technologycould be utilized for implementing structures shown in FIG. 2A-K.Various other types of layer transfer schemes that have been describedin Section 1.3.4 of the parent application (Ser. No. 12/901,890,8,026,521) can be utilized for construction of various 3D DRAMstructures. Furthermore, buried wiring, i.e. where wiring for memoryarrays is below the memory layers but above the periphery, may also beused. In addition, other variations of the monolithic 3D DRAM conceptsare possible.

While many of today's memory technologies rely on charge storage,several companies are developing non-volatile memory technologies basedon resistance of a material changing. Examples of these resistance-basedmemories include phase change memory, Metal Oxide memory, resistive RAM(RRAM), memristors, solid-electrolyte memory, ferroelectric RAM, MRAM,etc. Background information on these resistive-memory types is given in“Overview of candidate device technologies for storage-class memory,”IBM Journal of Research and Development, vol. 52, no.4.5, pp. 449-464,July 2008 by Burr, G. W.; Kurdi, B. N.; Scott, J. C.; Lam, C. H.;Gopalakrishnan, K.; Shenoy, R. S.

FIGS. 3A-J describe a novel memory architecture for resistance-basedmemories, and a procedure for its construction. The memory architectureutilizes junction-less transistors and has a resistance-based memoryelement in series with a transistor selector. No mask is utilized on a“per-memory-layer” basis for the monolithic 3D resistance change memory(or resistive memory) concept shown in FIG. 3A-J, and all other masksare shared between different layers. The process flow may includeseveral steps that occur in the following sequence.

Step (A): Peripheral circuits 302 are first constructed and above this alayer of silicon dioxide 304 is deposited. FIG. 3A shows a drawingillustration after Step (A).Step (B): FIG. 3B illustrates the structure after Step (B). A wafer ofn+ Silicon 308 has an oxide layer 306 grown or deposited above it.Following this, hydrogen is implanted into the n+ Silicon wafer at acertain depth indicated by 314. Alternatively, some other atomic speciessuch as Helium could be (co-)implanted. This hydrogen implanted n+Silicon wafer 308 forms the top layer 310. The bottom layer 312 mayinclude the peripheral circuits 302 with oxide layer 304. The top layer310 is flipped and bonded to the bottom layer 312 using oxide-to-oxidebonding.Step (C): FIG. 3C illustrates the structure after Step (C). The stack oftop and bottom wafers after Step (B) is cleaved at the hydrogen plane314 using either an anneal or a sideways mechanical force or othermeans. A CMP process is then conducted. A layer of silicon oxide 318 isthen deposited atop the n+ Silicon layer 316. At the end of this step, asingle-crystal n+Si layer 316 exists atop the peripheral circuits, andthis has been achieved using layer-transfer techniques.Step (D): FIG. 3D illustrates the structure after Step (D). Usingmethods similar to Step (B) and (C), multiple n+ silicon layers 320 areformed with silicon oxide layers in between.Step (E): FIG. 3E illustrates the structure after Step (E). Lithographyand etch processes are then utilized to make a structure as shown in thefigure, including layer regions of n+ silicon 321 and associatedbonding/isolation oxides 322.Step (F): FIG. 3F illustrates the structure after Step (F). Gatedielectric 326 and gate electrode 324 are then deposited following whicha CMP is performed to planarize the gate electrode 324 regions.Lithography and etch are utilized to define gate regions.Step (G): FIG. 3G illustrates the structure after Step (G). A siliconoxide layer 330 is then deposited and planarized. The silicon oxidelayer is shown transparent in the figure for clarity, along withword-line (WL) 332 and source-line (SL) 334 regions.Step (H): FIG. 3H illustrates the structure after Step (H). Vias areetched through multiple layers of silicon and silicon dioxide as shownin the figure. A resistance change memory material 336 is then deposited(preferably with atomic layer deposition (ALD)). Examples of such amaterial include hafnium oxide, well known to change resistance byapplying voltage. An electrode for the resistance change memory elementis then deposited (preferably using ALD) and is shown as electrode/BLcontact 340. A CMP process is then conducted to planarize the surface.It can be observed that multiple resistance change memory elements inseries with junctionless transistors are created after this step.Step (I): FIG. 3I illustrates the structure after Step (I). BLs 338 arethen constructed. Contacts are made to BLs, WLs and SLs of the memoryarray at its edges. SL contacts can be made into stair-like structuresusing techniques described in in “Bit Cost Scalable Technology withPunch and Plug Process for Ultra High Density Flash Memory,” VLSITechnology, 2007 IEEE Symposium on, vol., no., pp. 14-15, 12-14 Jun.2007 by Tanaka, H.; Kido, M.; Yahashi, K.; Oomura, M.; et al., followingwhich contacts can be constructed to them. Formation of stair-likestructures for SLs could be achieved in steps prior to Step (I) as well.FIG. 3J shows cross-sectional views of the array for clarity.A 3D resistance change memory has thus been constructed, with (1)horizontally-oriented transistors—i.e. current flowing in substantiallythe horizontal direction in transistor channels, (2) some of the memorycell control lines, e.g., source-lines SL, constructed of heavily dopedsilicon and embedded in the memory cell layer, (3) side gates that aresimultaneously deposited over multiple memory layers for transistors,and (4) monocrystalline (or single-crystal) silicon layers obtained bylayer transfer techniques such as ion-cut.

FIGS. 4A-4K describe an alternative process flow to construct ahorizontally-oriented monolithic 3D resistive memory array. Thisembodiment has a resistance-based memory element in series with atransistor selector. No mask is utilized on a “per-memory-layer” basisfor the monolithic 3D resistance change memory (or resistive memory)concept shown in FIGS. 4A-4K, and all other masks are shared betweendifferent layers. The process flow may include several steps asdescribed in the following sequence.

Step (A): Peripheral circuits with tungsten wiring 402 are firstconstructed and above this a layer of silicon dioxide 404 is deposited.FIG. 4A shows a drawing illustration after Step (A).Step (B): FIG. 4B illustrates the structure after Step (B). A wafer ofp-Silicon 408 has an oxide layer 406 grown or deposited above it.Following this, hydrogen is implanted into the p-Silicon wafer at acertain depth indicated by 414. Alternatively, some other atomic speciessuch as Helium could be (co-)implanted. This hydrogen implantedp-Silicon wafer 408 forms the top layer 410. The bottom layer 412 mayinclude the peripheral circuits 402 with oxide layer 404. The top layer410 is flipped and bonded to the bottom layer 412 using oxide-to-oxidebonding.Step (C): FIG. 4C illustrates the structure after Step (C). The stack oftop and bottom wafers after Step (B) is cleaved at the hydrogen plane414 using either a anneal or a sideways mechanical force or other means.A CMP process is then conducted. A layer of silicon oxide 418 is thendeposited atop the p-Silicon layer 416. At the end of this step, asingle-crystal p-Si layer 416 exists atop the peripheral circuits, andthis has been achieved using layer-transfer techniques.Step (D): FIG. 4D illustrates the structure after Step (D). Usingmethods similar to Step (B) and (C), multiple p-silicon layers 420 areformed with silicon oxide layers in between.Step (E): FIG. 4E illustrates the structure after Step (E). Lithographyand etch processes are then utilized to make a structure as shown in thefigure, including layer regions of p-silicon 421 and associatedbonding/isolation oxide 422.Step (F): FIG. 4F illustrates the structure on after Step (F). Gatedielectric 426 and gate electrode 424 are then deposited following whicha CMP is done to planarize the gate electrode 424 regions. Lithographyand etch are utilized to define gate regions.Step (G): FIG. 4G illustrates the structure after Step (G). Using thehard mask defined in Step (F), p-regions not covered by the gate areimplanted to form n+ silicon regions 428. Spacers are utilized duringthis multi-step implantation process and layers of silicon present indifferent layers of the stack have different spacer widths to accountfor lateral straggle of buried layer implants. Bottom layers could havelarger spacer widths than top layers. A thermal annealing step, such asa RTA or spike anneal or laser anneal or flash anneal, is then conductedto activate n+ doped regions.Step (H): FIG. 4H illustrates the structure after Step (H). A siliconoxide layer 430 is then deposited and planarized. The silicon oxidelayer is shown transparent in the figure for clarity, along withword-line (WL) 432 and source-line (SL) 434 regions.Step (I): FIG. 4I illustrates the structure after Step (I). Vias areetched through multiple layers of silicon and silicon dioxide as shownin the figure. A resistance change memory material 436 is then deposited(preferably with atomic layer deposition (ALD)). Examples of such amaterial include hafnium oxide, which is well known to change resistanceby applying voltage. An electrode for the resistance change memoryelement is then deposited (preferably using ALD) and is shown aselectrode/BL contact 440. A CMP process is then conducted to planarizethe surface. It can be observed that multiple resistance change memoryelements in series with transistors are created after this step.Step (J): FIG. 4J illustrates the structure after Step (J). BLs 438 arethen constructed. Contacts are made to BLs, WLs and SLs of the memoryarray at its edges. SL contacts can be made into stair-like structuresusing techniques described in “Bit Cost Scalable Technology with Punchand Plug Process for Ultra High Density Flash Memory,” VLSI Technology,2007 IEEE Symposium on, vol., no., pp. 14-15, 12-14 Jun. 2007 by Tanaka,H.; Kido, M.; Yahashi, K.; Oomura, M.; et al., following which contactscan be constructed to them. Formation of stair-like structures for SLscould be done in steps prior to Step (I) as well.FIG. 4K shows cross-sectional views of the array for clarity.

A 3D resistance change memory has thus been constructed, with (1)horizontally-oriented transistors—i.e. current flowing in substantiallythe horizontal direction in transistor channels, (2) some of the memorycell control lines—e.g., source-lines SL, constructed of heavily dopedsilicon and embedded in the memory cell layer, (3) side gatessimultaneously deposited over multiple memory layers for transistors,and (4) monocrystalline (or single-crystal) silicon layers obtained bylayer transfer techniques such as ion-cut.

While explanations have been given for formation of monolithic 3Dresistive memories with ion-cut in this section, it is clear to oneskilled in the art that alternative implementations are possible. BL andSL nomenclature has been used for two terminals of the 3D resistivememory array, and this nomenclature can be interchanged. Moreover,selective epi technology or laser recrystallization technology could beutilized for implementing structures shown in FIG. 3A-3J and FIG. 4A-4K.Various other types of layer transfer schemes that have been describedin Section 1.3.4 of the parent application can be utilized forconstruction of various 3D resistive memory structures. One could alsouse buried wiring, i.e. where wiring for memory arrays is below thememory layers but above the periphery. Other variations of themonolithic 3D resistive memory concepts are possible.

While resistive memories described previously form a class ofnon-volatile memory, others classes of non-volatile memory exist. NANDflash memory forms one of the most common non-volatile memory types. Itcan be constructed of two main types of devices: floating-gate deviceswhere charge is stored in a floating gate and charge-trap devices wherecharge is stored in a charge-trap layer such as Silicon Nitride.Background information on charge-trap memory can be found in “IntegratedInterconnect Technologies for 3D Nanoelectronic Systems”, Artech House,2009 by Bakir and Meindl (“Bakir”) and “A Highly Scalable 8-Layer 3DVertical-Gate (VG) TFT NAND Flash Using Junction-Free Buried ChannelBE-SONOS Device,” Symposium on VLSI Technology, 2010 by Hang-Ting Lue,et al. The architectures shown in FIG. 5A-5G are relevant for any typeof charge-trap memory.

FIGS. 5A-5G describes a memory architecture for single-crystal 3Dcharge-trap memories, and a procedure for its construction. It utilizesjunction-less transistors. No mask is utilized on a “per-memory-layer”basis for the monolithic 3D charge-trap memory concept shown in FIG.5A-5G, and all other masks are shared between different layers. Theprocess flow may include several steps as described in the followingsequence.

Step (A): Peripheral circuits 502 are first constructed and above this alayer of silicon dioxide 504 is deposited. FIG. 5A shows a drawingillustration after Step (A).Step (B): FIG. 5B illustrates the structure after Step (B). A wafer ofn+ Silicon 508 has an oxide layer 506 grown or deposited above it.Following this, hydrogen is implanted into the n+ Silicon wafer at acertain depth indicated by 514. Alternatively, some other atomic speciessuch as Helium could be implanted. This hydrogen implanted n+ Siliconwafer 508 forms the top layer 510. The bottom layer 512 may include theperipheral circuits 502 with oxide layer 504. The top layer 510 isflipped and bonded to the bottom layer 512 using oxide-to-oxide bonding.Step (C): FIG. 5C illustrates the structure after Step (C). The stack oftop and bottom wafers after Step (B) is cleaved at the hydrogen plane514 using either a anneal or a sideways mechanical force or other means.A CMP process is then conducted. A layer of silicon oxide 518 is thendeposited atop the n+ Silicon layer 516. At the end of this step, asingle-crystal n+Si layer 516 exists atop the peripheral circuits, andthis has been achieved using layer-transfer techniques.Step (D): FIG. 5D illustrates the structure after Step (D). Usingmethods similar to Step (B) and (C), multiple n+ silicon layers 520 areformed with silicon oxide layers in between.Step (E): FIG. 5E illustrates the structure after Step (E). Lithographyand etch processes are then utilized to make a structure as shown in thefigure.Step (F): FIG. 5F illustrates the structure after Step (F). Gatedielectric 526 and gate electrode 524 are then deposited following whicha CMP is done to planarize the gate electrode 524 regions. Lithographyand etch are utilized to define gate regions. Gates of the NAND string536 as well gates of select gates of the NAND string 538 are defined.Step (G): FIG. 5G illustrates the structure after Step (G). A siliconoxide layer 530 is then deposited and planarized. It is showntransparent in the figure for clarity. Word-lines, bit-lines andsource-lines are defined as shown in the figure. Contacts are formed tovarious regions/wires at the edges of the array as well. SL contacts canbe made into stair-like structures using techniques described in “BitCost Scalable Technology with Punch and Plug Process for Ultra HighDensity Flash Memory,” VLSI Technology, 2007 IEEE Symposium on, vol.,no., pp. 14-15, 12-14 Jun. 2007 by Tanaka, H.; Kido, M.; Yahashi, K.;Oomura, M.; et al., following which contacts can be constructed to them.Formation of stair-like structures for SLs could be performed in stepsprior to Step (G) as well.A 3D charge-trap memory has thus been constructed, with (1)horizontally-oriented transistors—i.e. current flowing in substantiallythe horizontal direction in transistor channels, (2) some of the memorycell control lines—e.g., bit lines BL, constructed of heavily dopedsilicon and embedded in the memory cell layer, (3) side gatessimultaneously deposited over multiple memory layers for transistors,and (4) monocrystalline (or single-crystal) silicon layers obtained bylayer transfer techniques such as ion-cut. This use of single-crystalsilicon obtained with ion-cut is a key differentiator from past work on3D charge-trap memories such as “A Highly Scalable 8-Layer 3DVertical-Gate (VG) TFT NAND Flash Using Junction-Free Buried ChannelBE-SONOS Device,” Symposium on VLSI Technology, 2010 by Hang-Ting Lue,et al. that used polysilicon.

While FIGS. 5A-5G give two examples of how single-crystal silicon layerswith ion-cut can be used to produce 3D charge-trap memories, the ion-cuttechnique for 3D charge-trap memory is fairly general. It could beutilized to produce any horizontally-oriented 3D monocrystalline-siliconcharge-trap memory.

While the 3D DRAM and 3D resistive memory implementations in Section 3and Section 4 have been described with single crystal siliconconstructed with ion-cut technology, other options exist. One couldconstruct them with selective epi technology. Procedures for doing thesewill be clear to those skilled in the art.

FIGS. 6A-6B show it is not the only option for the architecture to havethe peripheral transistors, such as periphery 602, below the memorylayers, including, for example, memory layer 604, memory layer 606,and/or memory layer 608. Peripheral transistors, such as periphery 610,could also be constructed above the memory layers, including, forexample, memory layer 604, memory layer 606, and/or memory layer 608,and substrate or memory layer 612, as shown in FIG. 6B. This peripherylayer would utilize technologies described in this application; parentapplication and incorporated references, and could utilize transistors,for example, junction-less transistors or recessed channel transistors.

The monolithic 3D integration concepts described in this patentapplication can lead to novel embodiments of poly-silicon-based memoryarchitectures as well. Poly silicon based architectures couldpotentially be cheaper than single crystal silicon based architectureswhen a large number of memory layers need to be constructed. While thebelow concepts are explained by using resistive memory architectures asan example, it will be clear to one skilled in the art that similarconcepts can be applied to NAND flash memory and DRAM architecturesdescribed previously in this patent application.

FIGS. 7A-7E show one embodiment of the current invention, wherepolysilicon junction-less transistors are used to form a 3Dresistance-based memory. The utilized junction-less transistors can haveeither positive or negative threshold voltages. The process may includethe following steps as described in the following sequence:

Step (A): As illustrated in FIG. 7A, peripheral circuits 702 areconstructed above which a layer of silicon dioxide 704 is made.Step (B): As illustrated in FIG. 7B, multiple layers of n+ dopedamorphous silicon or polysilicon 706 are deposited with layers ofsilicon dioxide 708 in between. The amorphous silicon or polysiliconlayers 706 could be deposited using a chemical vapor deposition process,such as LPCVD or PECVD.Step (C): As illustrated in FIG. 7C, a Rapid Thermal Anneal (RTA) isconducted to crystallize the layers of polysilicon or amorphous silicondeposited in Step (B). Temperatures during this RTA could be as high as700° C. or more, and could even be as high as 800° C. The polysiliconregion obtained after Step (C) is indicated as 710. Alternatively, alaser anneal could be conducted, either for all layers 706 at the sametime or layer by layer. The thickness of the oxide 704 would need to beoptimized if that process were conducted.Step (D): As illustrated in FIG. 7D, procedures similar to thosedescribed in FIGS. 3E-3H are utilized to construct the structure shown.The structure in FIG. 7D has multiple levels of junction-less transistorselectors for resistive memory devices. The resistance change memory isindicated as 736 while its electrode and contact to the BL is indicatedas 740. The WL is indicated as 732, while the SL is indicated as 734.Gate dielectric of the junction-less transistor is indicated as 726while the gate electrode of the junction-less transistor is indicated as724, this gate electrode also serves as part of the WL 732. Siliconoxide is indicated as 730.Step (E): As illustrated in FIG. 7E, bit lines (indicated as BL 738) areconstructed. Contacts are then made to peripheral circuits and variousparts of the memory array as described in embodiments describedpreviously.

FIG. 8A-F show another embodiment of the current invention, wherepolysilicon junction-less transistors are used to form a 3Dresistance-based memory. The utilized junction-less transistors can haveeither positive or negative threshold voltages. The process may includethe following steps occurring in sequence:

Step (A): As illustrated in FIG. 8A, a layer of silicon dioxide 804 isdeposited or grown above a silicon substrate without circuits 802.Step (B): As illustrated in FIG. 8B, multiple layers of n+ dopedamorphous silicon or polysilicon 806 are deposited with layers ofsilicon dioxide 808 in between. The amorphous silicon or polysiliconlayers 806 could be deposited using a chemical vapor deposition process,such as LPCVD or PECVD abbreviated as above.Step (C): As illustrated in FIG. 8C, a Rapid Thermal Anneal (RTA) orstandard anneal is conducted to crystallize the layers of polysilicon oramorphous silicon deposited in Step (B). Temperatures during this RTAcould be as high as 700° C. or more, and could even be as high as 1400°C. The polysilicon region obtained after Step (C) is indicated as 810.Since there are no circuits under these layers of polysilicon, very hightemperatures (such as 1400° C.) can be used for the anneal process,leading to very good quality polysilicon with few grain boundaries andvery high mobilities approaching those of single crystal silicon.Alternatively, a laser anneal could be conducted, either for all layers806 at the same time or layer by layer at different times.Step (D): This is illustrated in FIG. 8D. Procedures similar to thosedescribed in FIG. 32E-H of incorporated parent reference U.S. Pat. No.8,026,521, are utilized to obtain the structure shown in FIG. 8D whichhas multiple levels of junctionless transistor selectors for resistivememory devices. The resistance change memory is indicated as 836 whileits electrode and contact to the BL is indicated as 840. The WL isindicated as 832, while the SL is indicated as 834. Gate dielectric ofthe junction-less transistor is indicated as 826 while the gateelectrode of the junction-less transistor is indicated as 824, this gateelectrode also serves as part of the WL 832. Silicon oxide is indicatedas 830Step (E): This is illustrated in FIG. 8E. Bit lines (indicated as BL838) are constructed. Contacts are then made to peripheral circuits andvarious parts of the memory array as described in embodiments describedpreviously.Step (F): Using procedures described in Section 1 and Section 2 of thispatent application's parent, peripheral circuits 898 (with transistorsand wires) could be formed well aligned to the multiple memory layersshown in Step (E). For the periphery, one could use the process flowshown in Section 2 where replacement gate processing is used, or onecould use sub −400° C. processed transistors such as junction-lesstransistors or recessed channel transistors. Alternatively, one coulduse laser anneals for peripheral transistors′ source-drain processing.Various other procedures described in Section 1 and Section 2 could alsobe used. Connections can then be formed between the multiple memorylayers and peripheral circuits. By proper choice of materials for memorylayer transistors and memory layer wires (e.g., by using tungsten andother materials that withstand high temperature processing for wiring),even standard transistors processed at high temperatures (>1000° C.) forthe periphery could be used.

Section 1, of incorporated parent reference U.S. Pat. No. 8,026,521,described the formation of 3D stacked semiconductor circuits and chipswith sub −400° C. processing temperatures to build transistors and highdensity of vertical connections. In this section an alternative methodis explained, in which a transistor is built with any replacement gate(or gate-last) scheme that is utilized widely in the industry. Thismethod allows for high temperatures (above 400C) to build thetransistors. This method utilizes a combination of three concepts:

-   -   Replacement gate (or gate-last) high k/metal gate fabrication    -   Face-up layer transfer using a carrier wafer    -   Misalignment tolerance techniques that utilize regular or        repeating layouts. In these repeating layouts, transistors could        be arranged in substantially parallel bands.        A very high density of vertical connections is possible with        this method. Single crystal silicon (or monocrystalline silicon)        layers that are transferred are less than 2 um thick, or could        even be thinner than 0.4 um or 0.2 um.

The method mentioned in the previous paragraph is described in FIG.9A-9F. The procedure may include several steps as described in thefollowing sequence:

Step (A): After creating isolation regions using ashallow-trench-isolation (STI) process 2504, dummy gates 2502 areconstructed with silicon dioxide and poly silicon. The term “dummygates” is used since these gates will be replaced by high k gatedielectrics and metal gates later in the process flow, according to thestandard replacement gate (or gate-last) process. Further details ofreplacement gate processes are described in “A 45 nm Logic Technologywith High-k+Metal Gate Transistors, Strained Silicon, 9 Cu InterconnectLayers, 193 nm Dry Patterning, and 100% Pb-free Packaging,” IEDM Tech.Dig., pp. 247-250, 2007 by K. Mistry, et al. and “Ultralow-EOT (5 Å)Gate-First and Gate-Last High Performance CMOS Achieved byGate-Electrode Optimization,” IEDM Tech. Dig., pp. 663-666, 2009 by L.Ragnarsson, et al. FIG. 9A illustrates the structure after Step (A).

Step (B): Rest of the transistor fabrication flow proceeds withformation of source-drain regions 2506, strain enhancement layers toimprove mobility, high temperature anneal to activate source-drainregions 2506, formation of inter-layer dielectric (ILD) 2508, etc. FIG.9B illustrates the structure after Step (B).

Step (C): Hydrogen is implanted into the wafer at the dotted lineregions indicated by 2510. FIG. 9C illustrates the structure after Step(C).

Step (D): The wafer after step (C) is bonded to a temporary carrierwafer 2512 using a temporary bonding adhesive 2514. This temporarycarrier wafer 2512 could be constructed of glass. Alternatively, itcould be constructed of silicon. The temporary bonding adhesive 2514could be a polymer material, such as a polyimide. A anneal or a sidewaysmechanical force is utilized to cleave the wafer at the hydrogen plane2510. A CMP process is then conducted. FIG. 9D illustrates the structureafter Step (D).

Step (E): An oxide layer 2520 is deposited onto the bottom of the wafershown in Step (D). The wafer is then bonded to the bottom layer of wiresand transistors 2522 using oxide-to-oxide bonding. The bottom layer ofwires and transistors 2522 could also be called a base wafer. Thetemporary carrier wafer 2512 is then removed by shining a laser onto thetemporary bonding adhesive 2514 through the temporary carrier wafer 2512(which could be constructed of glass). Alternatively, an anneal could beused to remove the temporary bonding adhesive 2514. Through-siliconconnections 2516 with a non-conducting (e.g. oxide) liner 2515 to thelanding pads 2518 in the base wafer could be constructed at a very highdensity using special alignment methods described in at least FIG. 26A-Dand FIG. 27A-F of incorporated parent reference U.S. Pat. No. 8,026,521.FIG. 9E illustrates the structure after Step (E).

Step (F): Dummy gates 2502 are etched away, followed by the constructionof a replacement with high k gate dielectrics 2524 and metal gates 2526.Essentially, partially-formed high performance transistors are layertransferred atop the base wafer (may also be called target wafer)followed by the completion of the transistor processing with a low (sub400° C.) process. FIG. 9F illustrates the structure after Step (F). Theremainder of the transistor, contact, and wiring layers are thenconstructed.

It will be obvious to someone skilled in the art that alternativeversions of this flow are possible with various methods to attachtemporary carriers and with various versions of the gate-last processflow.

FIGS. 10A-10D (and FIG. 45A-D of incorporated parent reference U.S. Pat.No. 8,026,521) show an alternative procedure for forming CMOS circuitswith a high density of connections between stacked layers. The processutilizes a repeating pattern in one direction for the top layer oftransistors. The procedure may include several steps in the followingsequence:

Step (A): Using procedures similar to FIG. 9A-F, a top layer oftransistors 4404 is transferred atop a bottom layer of transistors andwires 4402. Landing pads 4406 are utilized on the bottom layer oftransistors and wires 4402. Dummy gates 4408 and 4410 are utilized fornMOS and pMOS. The key difference between the structures shown in FIG.9A-F and this structure is the layout of oxide isolation regions betweentransistors. FIG. 10A illustrates the structure after Step (A).

Step (B): Through-silicon connections 4412 are formed well-aligned tothe bottom layer of transistors and wires 4402. Alignment schemes to bedescribed in FIG. 45A-D of incorporated parent reference U.S. Pat. No.8,026,521 are utilized for this purpose. All features constructed infuture steps are also formed well-aligned to the bottom layer oftransistors and wires 4402. FIG. 10B illustrates the structure afterStep (B).

Step (C): Oxide isolation regions 4414 are formed between adjacenttransistors to be defined. These isolation regions are formed bylithography and etch of gate and silicon regions and then fill withoxide. FIG. 10C illustrates the structure after Step (C).

Step (D): The dummy gates 4408 and 4410 are etched away and replacedwith replacement gates 4416 and 4418. These replacement gates arepatterned and defined to form gate contacts as well. FIG. 10Dillustrates the structure after Step (D). Following this, other processsteps in the fabrication flow proceed as usual.

FIGS. 11A-11G illustrate using a carrier wafer for layer transfer. FIG.11A illustrates the first step of preparing transistors with dummy gates4602 on first donor wafer (or top wafer) 4606. This completes the firstphase of transistor formation.

FIG. 11B illustrates forming a cleave line 4608 by implant 4616 ofatomic particles such as H+. FIG. 11C illustrates permanently bondingthe first donor wafer 4606 to a second donor wafer 4626. The permanentbonding may be oxide to oxide wafer bonding as described previously.

FIG. 11D illustrates the second donor wafer 4626 acting as a carrierwafer after cleaving the first donor wafer off potentially at face 4632;leaving a thin layer 4606 with the now buried dummy gate transistors4602. FIG. 11E illustrates forming a second cleave line 4618 in thesecond donor wafer 4626 by implant 4646 of atomic species such as H+.

FIG. 11F illustrates the second layer transfer step to bring the dummygate transistors 4602 ready to be permanently bonded on top of thebottom layer of transistors and wires 4601. For the simplicity of theexplanation we left out the now obvious steps of surface layerpreparation done for each of these bonding steps.

FIG. 11G illustrates the bottom layer of transistors and wires 4601 withthe dummy gate transistor 4602 on top after cleaving off the seconddonor wafer and removing the layers on top of the dummy gatetransistors. Now we can proceed and replace the dummy gates with thefinal gates, form the metal interconnection layers, and continue the 3Dfabrication process.

An interesting alternative is available when using the carrier waferflow described in FIG. 11A-11G. In this flow we can use the two sides ofthe transferred layer to build NMOS on one side and PMOS on the otherside. Timing properly the replacement gate step such flow could enablefull performance transistors properly aligned to each other. Asillustrated in FIG. 12A, an SOI (Silicon On Insulator) donor (or top)wafer 4700 may be processed in the normal state of the art high k metalgate gate-last manner with adjusted thermal cycles to compensate forlater thermal processing up to the step prior to where CMP exposure ofthe polysilicon dummy gates 4704 takes place. FIG. 12A illustrates across section of the SOI donor wafer substrate 4700, the buried oxide(BOX) 4701, the thin silicon layer 4702 of the SOI wafer, the isolation4703 between transistors, the polysilicon 4704 and gate oxide 4705 ofn-type CMOS transistors with dummy gates, their associated source anddrains 4706 for NMOS, NMOS transistor channel regions 4707, and the NMOSinterlayer dielectric (ILD) 4708. Alternatively, the PMOS device may beconstructed at this stage. This completes the first phase of transistorformation.

At this step, or alternatively just after a CMP of layer 4708 to exposethe polysilicon dummy gates 4704 or to planarize the oxide layer 4708and not expose the dummy gates 4704, an implant of an atomic species4710, such as H+, is done to prepare the cleaving plane 4712 in the bulkof the donor substrate, as illustrated in FIG. 12B.

The SOI donor wafer 4700 is now permanently bonded to a carrier wafer4720 that has been prepared with an oxide layer 4716 for oxide to oxidebonding to the donor wafer surface 4714 as illustrated in FIG. 12C. Thedetails have been described previously. The donor wafer 4700 may then becleaved at the cleaving plane 4712 and may be thinned by chemicalmechanical polishing (CMP) and surface 4722 may be prepared fortransistor formation. The donor wafer layer 4700 at surface 4722 may beprocessed in the normal state of the art gate last processing to formthe PMOS transistors with dummy gates. During processing the wafer isflipped so that surface 4722 is on top, but for illustrative purposesthis is not shown in the subsequent FIGS. 12E-12G.

FIG. 12E illustrates the cross section with the buried oxide (BOX) 4701,the now thin silicon layer 4700 of the SOI substrate, the isolation 4733between transistors, the polysilicon 4734 and gate oxide 4735 of p-typeCMOS dummy gates, their associated source and drains 4736 for PMOS, PMOStransistor channel regions 4737 and the PMOS interlayer dielectric (ILD)4738. The PMOS transistors may be precisely aligned at state of the arttolerances to the NMOS transistors due to the shared substrate 4700possessing the same alignment marks. At this step, or alternatively justafter a CMP of layer 4738 to expose the PMOS polysilicon dummy gates orto planarize the oxide layer 4738 and not expose the dummy gates, thewafer could be put into high temperature cycle to activate both thedopants in the NMOS and the PMOS source drain regions.

Then an implant of an atomic species 4740, such as H+, may prepare thecleaving plane 4721 in the bulk of the carrier wafer substrate 4720 forlayer transfer suitability, as illustrated in FIG. 12F. The PMOStransistors are now ready for normal state of the art gate-lasttransistor formation completion.

As illustrated in FIG. 12G, the inter layer dielectric 4738 may bechemical mechanically polished to expose the top of the polysilicondummy gates 4734. The dummy polysilicon gates 4734 may then be removedby etch and the PMOS hi-k gate dielectric 4740 and the PMOS specificwork function metal gate 4741 may be deposited. An aluminum fill 4742may be performed on the PMOS gates and the metal CMP′ed. A dielectriclayer 4739 may be deposited and the normal gate 4743 and source/drain4744 contact formation and metallization.

The PMOS layer to NMOS layer via 4747 and metallization may be partiallyformed as illustrated in FIG. 12G and an oxide layer 4748 is depositedto prepare for bonding.

The carrier wafer and two sided n/p layer is then permanently bonded tobottom wafer having transistors and wires 4799 with associated metallanding strip 4750 as illustrated in FIG. 12H.

The carrier wafer 4720 may then be cleaved at the cleaving plane 4721and may be thinned by chemical mechanical polishing (CMP) to oxide layer4716 as illustrated in FIG. 12I.

The NMOS transistors are now ready for normal state of the art gate-lasttransistor formation completion. As illustrated in FIG. 12J, the oxidelayer 4716 and the NMOS inter layer dielectric 4708 may be chemicalmechanically polished to expose the top of the NMOS polysilicon dummygates 4704. The dummy polysilicon gates 4704 may then be removed by etchand the NMOS hi-k gate dielectric 4760 and the NMOS specific workfunction metal gate 4761 may be deposited. An aluminum fill 4762 may beperformed on the NMOS gates and the metal CMP′ed. A dielectric layer4769 may be deposited and the normal gate 4763 and source/drain 4764contact formation and metallization. The NMOS layer to PMOS layer via4767 to connect to 4747 and metallization may be formed.

As illustrated in FIG. 12K, the layer-to-layer contacts 4772 to thelanding pads in the base wafer are now made. This same contact etchcould be used to make the connections 4773 between the NMOS and PMOSlayer as well, instead of using the two step (4747 and 4767) method inFIG. 12H.

Using procedures similar to FIG. 12A-K, it is possible to constructstructures such as FIG. 13 where a transistor is constructed with frontgate 4902 and back gate 4904. The back gate could be utilized for manypurposes such as threshold voltage control, reduction of variability,increase of drive current and other purposes.

It will also be appreciated by persons of ordinary skill in the art thatthe invention is not limited to what has been particularly shown anddescribed hereinabove. For example, drawings or illustrations may notshow n or p wells for clarity in illustration. Further, combinations andsub-combinations of the various features described hereinabove may beutilized to form a 3D IC based system. Rather, the scope of theinvention includes both combinations and sub-combinations of the variousfeatures described hereinabove as well as modifications and variationswhich would occur to such skilled persons upon reading the foregoingdescription. Thus the invention is to be limited only by the appendedclaims.

What is claimed is:
 1. A 3D semiconductor device, the device comprising:a first level comprising a first single crystal layer and firsttransistors, wherein said first transistors each comprise a singlecrystal channel; first metal layers interconnecting at least said firsttransistors; and a second level comprising a second single crystal layerand second transistors, wherein said second level overlays said firstlevel, wherein said second transistors are horizontally oriented andcomprise a gate dielectric, wherein said gate dielectric compriseshafnium oxide, wherein said second level is bonded to said first level,and wherein said bonded comprises oxide to oxide bonds.
 2. The deviceaccording to claim 1, wherein said at least one of said secondtransistors is a Recessed Channel Array Transistor (“RCAT”).
 3. Thedevice according to claim 1, wherein said second transistors eachcomprise at least two side-gates.
 4. The device according to claim 1,wherein at least one of said second transistors is an N-type transistor,and wherein at least one of said second transistors is a P-typetransistor.
 5. The device according to claim 1, wherein said first levelcomprises third transistors and fourth transistors, wherein said fourthtransistors are overlying said third transistors, and wherein said thirdtransistors and said fourth transistors are self-aligned, beingprocessed following the same lithography step.
 6. The device accordingto claim 1, wherein said bonded comprises metal to metal bonds.
 7. Thedevice according to claim 1, wherein said second level comprises amemory array, and wherein said first level comprises control circuitscontrolling data written to said memory array.
 8. A 3D semiconductordevice, the device comprising: a first level comprising a first singlecrystal layer and first transistors, wherein said first transistors eachcomprise a single crystal channel; first metal layers interconnecting atleast said first transistors; and a second level comprising a secondsingle crystal layer and second transistors, wherein said second leveloverlays said first level, wherein said second transistors arehorizontally oriented, wherein said at least one of said secondtransistors is a Recessed Channel Array Transistor (“RCAT”), whereinsaid second level is bonded to said first level, and wherein said bondedcomprises oxide to oxide bonds.
 9. The device according to claim 8,wherein said at least one of said second transistor comprises a gatedielectric, and wherein said gate dielectric comprises hafnium oxide.10. The device according to claim 8, wherein said second transistorseach comprise at least two side-gates.
 12. The device according to claim8, further comprising: a second metal layer and a third metal layer,wherein said second metal layer is disposed above said first metallayers, wherein said third metal layer is above said second metal layerand below said second single crystal layer, wherein said second metalcomprises a first thickness and said third metal comprises a secondthickness, and wherein said first thickness is significantly greaterthan said second thickness.
 13. The device according to claim 8, whereinsaid bonded comprises metal to metal bonds.
 14. The device according toclaim 8, wherein said second level comprises a memory array, and whereinsaid first level comprises control circuits controlling data written tosaid memory array.
 15. A 3D semiconductor device, the device comprising:a first level comprising a first single crystal layer and firsttransistors, wherein said first transistors each comprise a singlecrystal channel; first metal layers interconnecting at least said firsttransistors; a second level comprising a second single crystal layer andsecond transistors, wherein said second level overlays said first level;and a second metal layer and a third metal layer, wherein said secondmetal layer is disposed above said first metal layer, wherein said thirdmetal layer is above said second metal layer and below said secondsingle crystal layer, wherein said second metal comprises a firstthickness and said third metal comprises a second thickness, whereinsaid first thickness is significantly greater than said secondthickness, wherein said second level is bonded to said first level, andwherein said bonded comprises oxide to oxide bonds.
 16. The deviceaccording to claim 15, wherein at least one of said second transistorsis a Recessed Channel Array Transistor (“RCAT”).
 17. The deviceaccording to claim 15, wherein said second transistors each comprise atleast two side-gates.
 18. The device according to claim 15, wherein saidsecond transistors are horizontally oriented and comprise a gatedielectric, and wherein said gate dielectric comprises hafnium oxide.19. The device according to claim 15, wherein said bonded comprisesmetal to metal bonds.
 20. The device according to claim 15, wherein saidsecond level comprises a memory array, and wherein said first levelcomprises control circuits controlling data written to said memoryarray.